| 1. |
- Aitomäki, Yvonne, et al.
(författare)
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Vacuum infusion of cellulose nanofibre network composites : Influence of porosity on permeability and impregnation
- 2016
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 95, s. 204-211
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Tidskriftsartikel (refereegranskat)abstract
- Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.
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| 2. |
- Aitomäki, Yvonne, et al.
(författare)
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Vacuum Infusion of Nanocellulose Networks of Different Porosity
- 2015
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Ingår i: 20th International Conference on Composite Materials. - : ICCM.
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Konferensbidrag (refereegranskat)abstract
- Cellulose nanofibres (CNF) have shown good potential as sustainable, biobased reinforcing materials in polymer composites. Addressing issues around the processing of these composites is an important part of establishing their use in different applications. Here, CNF networks of different porosity are made from nanofibrillated hardwood kraft pulp with the aim of increasing the impregnation of the CNF networks and to allow vacuum infusion to be used. Two different vacuum infusion strategies: in-plane and out of plane were used to infuse the CNF networks with a low viscosity epoxy. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated and compared to a micro-fibre based network. Using the out-of-plane permeability measurements and Darcy’s law, the fill-time was calculated and showed that the CNF network with 40% porosity had the lowest fill-time when an out-of-plane impregnation strategy is used. However this exceeded the gel-time of the epoxy system. In experiments, the resin reached the other side of the network but low transparency indicated that wetting was poor. The dry CNF preforms showed a very strong dependence on the porosity with both modulus and strength increasing rapidly at low porosity. Interestingly, the composite based on the 60% porosity network showed good wetting particularly with the in-plane infusion strategy, exhibiting a much more brittle fracture and a high yield strength. This shows that in CNF composites produced by VI, lowering the fibre volume content of the CNF composites gives better impregnation resulting in a lower ultimate strength but higher yield strength and no loss in modulus.
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| 3. |
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| 4. |
- Almqvist, Andreas, et al.
(författare)
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Flow in thin domains with a microstructure : Lubrication and thin porous media
- 2017
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Ingår i: AIP Conference Proceedings. - : AIP Publishing. - 0094-243X .- 1551-7616. ; 1798
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Tidskriftsartikel (refereegranskat)abstract
- This paper is devoted to homogenization of different models of flow in thin domains with a microstructure. The focus is on applications connected to the effect of surface roughness in full film lubrication, but a parallel to flow in thin porous media is also discussed. Mathematical models of such flows naturally include two small parameters. One is connected to the fluid film thickness and the other to the microstructure. The corresponding asymptotic analysis is a delicate problem, since the result depends on how fast the two small parameters tend to zero relative to each other. We give a review of the current status in this area and point out some future challenges.
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| 5. |
- Alnersson, Gustaf, et al.
(författare)
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3D-flow and and fibre orientation modelling for compression moulding of SMC
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Two different numerical models for compression moulding of Sheet Moulding Compound are discussed and compared, with one being a more traditional flow model implemented in the 3DTimon commercial software, and the other being a more advanced flow model implemented in more general fluid dynamics software. The focus will be on comparing the resulting fibre orientations.
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| 6. |
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| 7. |
- Alnersson, Gustaf, et al.
(författare)
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3D flow and fibre orientation modelling of compression moulding of A-SMC: simulations and experimental validation in squeeze flow
- 2023
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Ingår i: Functional Composite Materials. - : Springer Nature. - 2522-5774. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Sheet Moulding Compound (SMC) based composites have a large potential in industrial contexts due to the possibility of achieving comparatively short manufacturing times. It is however necessary to be able to numerically predict both mechanical properties as well as manufacturability of parts.In this paper a fully 3D, semi-empirical model based on fluid mechanics for the compression moulding of SMC is described and discussed, in which the fibres and the resin are modelled as a single, inseparable fluid with a viscosity that depends on volume fraction of fibres, shear strain rate and temperature. This model is applied to an advanced carbon-fibre SMC with a high fibre volume fraction (35%). Simulations are run on a model of a squeeze test rig, allowing comparison to experimental results from such a rig. The flow data generated by this model is then used as input for an Advani-Tucker type of model for the evolution of the fibre orientation during the pressing process. Numerical results are also obtained from the software 3DTimon. The resulting fibre orientation distributions are then compared to experimental results that are obtained from microscopy. The experimental measurement of the orientation tensors is performed using the Method of Ellipses. A new, automated, accurate and fast method for the ellipse fitting is developed using machine learning. For the studied case, comparison between the experimental results and numerical methods indicate that 3D Timon better captures the random orientation at the outer edges of the circular disc, while 3D CFD show larger agreement in terms of the out-of-plane component. One of the advantages of the new image technique is that less work is required to obtain microscope images with a quality good enough for the analysis.
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| 8. |
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| 9. |
- Alnersson, Gustaf, et al.
(författare)
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Numerical Study of the 3D-Flow Characteristics During Compression Moulding of SMC
- 2019
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Ingår i: Proceedings of the 2019 International Conference on Composite Materials. - : RMIT University. ; , s. 1571-1581
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A numerical model for compression moulding of Sheet Moulding Compound is presented. The model is based on fluid mechanics and the SMC charge is modelled as a fluid with a viscosity that is dependent on the charge temperature, the fibre volume fraction of the material and the shear strain rate. Trends observed in the simulations regarding the shape of the flow front agree with experimental observations in previous studies. The simulations also yield that the type and magnitude of initial heating effects the initial flow to a large extent.
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| 10. |
- Alnersson, Gustaf, et al.
(författare)
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Review of the Numerical Modeling of Compression Molding of Sheet Molding Compound
- 2020
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Ingår i: Processes. - : MDPI. - 2227-9717. ; 8:2
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Forskningsöversikt (refereegranskat)abstract
- A review of the numerical modeling of the compression molding of the sheet molding compound (SMC) is presented. The focus of this review is the practical difficulties of modeling cases with high fiber content, an area in which there is relatively little documented work. In these cases, the prediction of the flows become intricate due to several reasons, mainly the complex rheology of the compound and large temperature gradients, but also the orientation of fibers and the micromechanics of the interactions between the fluid and the fibers play major roles. The details of this during moldings are discussed. Special attention is given to the impact on viscosity from the high fiber volume fraction, and the various models for this. One additional area of interest is the modeling of the fiber orientation.
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